The invention relates generally to transmission of radio frequency signals (e.g., SDARS signals) from an antenna across a dielectric such as glass to a receiver disposed in a vehicle, as well as the transmission across glass of power from the receiver to antenna electronics. The invention also relates to an antenna system having DC and RF coupling across a dielectric which uses a relatively low supply voltage and low loss circuit boards and patch arrangement for optimal RF coupling.
With reference to FIG. 1, a number of antenna systems have been proposed which provide for the transfer of radio frequency (RF) energy through glass or other dielectric surface to avoid having to drill holes, for example, through the windshield or window of an automobile for installation. Glass-mount antenna systems ate advantageous because they obviate the necessity of having to provide a proper seal around an installation hole or other window opening in order to protect the interior of the vehicle and its occupants from exposure to external weather conditions.
In the conventional antenna system 20 depicted in FIG. 1, RF signals from an antenna 22 are conducted across a glass surface 24 via a coupling device 26 that typically employs capacitive coupling, slot coupling or aperture coupling. The portion of the coupling device 26 on the interior of the vehicle is connected to a matching circuit 28 which provides the RF signals to a low noise amplifier (LNA) 32 at the input of a receiver 34 via an RF or coaxial cable 30. The matching circuit 28 can comprise passive components or traces on a circuit board, for example. The antenna system 20 is disadvantageous because the matching circuit 28, losses associated with the cable 30 and RF coupling (e.g., on the order of 2 to 4 dB or more) cause an increase in system noise. RF coupling losses increase as frequency increases. To reduce coupling losses, a conventional antenna system 20 is preferably implemented using ceramic compositions for circuit boards that are relatively expensive (e.g., Rogers 3003, 4003, 3010, and the like available from Rogers Corporation, Chandler, Ariz.). The cost associated with using these types of materials is 5 times that of a standard FR4 circuit board. A need therefore exists for an antenna system that achieves low RF coupling loss using low cost circuit boards.
Another proposed antenna system 40, which is described with reference to FIG. 2, has an RF coupling device similar to that used in the antenna system 20 depicted in FIG. 1, as well as DC coupling components to provide power to the antenna electronic circuitry. The antenna system 40 is configured to transmit video signals from satellite antenna electronics through a glass window 46 into a structure such as a residence or office building without requiring a hole through the glass. An exterior module 42 is mounted, for example, on the exterior of the structure, while an interior module 44 and receiver 48 are provided within the structure. RF coupling units 50a and 50b are provided on opposite sides of the glass 46 which is typically a window in the building. RF coupling unit 50b is connected to the exterior module 42 via a coaxial cable 54 to allow the exterior module 42 to be located remotely therefrom (e.g., on the building rooftop). The exterior module 42 encloses an antenna 52 and associated electronics (e.g., an LNA 56) to receive RF signals, which are then provided from the LNA 56 to the coupling device 50b via the cable 54 for transfer through the glass 46.
With continued reference to FIG. 2, RF energy transferred through the glass 46 is processed via a matching circuit 58. The matching circuit 28 is connected to a receiver 48 by another coaxial cable 60. In addition, DC power is provided from the interior module 44 to the exterior module 42 (e.g., to provide power for the LNA 48) by low frequency coupling coils 62a and 62b mounted opposite each other on either side of the glass 46. In a conventional satellite TV system, electrical power for the satellite antenna electronics is provided from the receiver 48 on the same coaxial cable that provides video signals from the antenna 52 to the receiver 48.
While the provision of DC power to antenna electronics is useful, the matching circuit and cable losses associated with the antenna system 40 are not desirable for such applications as a Satellite Digital Audio Radio Services (SDARS) system antenna for a vehicle. At 800 MHz, the coupling loss experienced with conventional glass mount antenna arrangements can be as much as 3 dB. At higher frequencies, the coupling loss increases substantially. For such high frequency applications as satellite radio operating at 2.4 GHz, the coupling loss is expected to be unacceptably high (e.g., 2 to 4 dB), making reception difficult. A need therefore exists for a glass or other dielectric-mounted antenna arrangement for high frequency wireless communication applications, and particularly, satellite radio applications, that reduces coupling loss and that is also compact.
Further, noise temperature is a significant parameter in an antenna system such as one that receives a satellite signal which is then amplified by an LNA. The noise temperature needs to be as low as possible. A need therefore exists for an antenna system that achieves that transfer of DC power across a dielectric (e.g., from the inside to the outside of a vehicle through the windshield) without significant degradation on system noise temperature.
The above described disadvantages are overcome and a number of advantages ate realized by an antenna system whereby RF coupling devices for mounting on opposite sides of a dielectric are made of low cost and low loss materials, and the transfer of RF energy across the dielectric occurs without significant degradation due to increased system noise.
The RF coupling devices ate also compact in design. Quarterwave patches are mounted on a circuit board and attached to a dielectric such that the patch is against the dielectric. The patch is provided with one or mote feeds, depending on the number of RF signals to be processed.
In accordance with another aspect of the present invention, the antenna system achieves DC coupling across the dielectric even though the supply voltage (e.g., the voltage supplied from a tuner to an antenna module located on the opposite side of a dielectric) is relatively low (e.g., 5 volts, as opposed to between 12 and 18 volts).
In accordance with an embodiment of the present invention, a DC voltage supplied on one side of a dielectric is increased to a higher voltage and then converted to an AC voltage to transfer electrical power across a dielectric via magnetic inductance.
In accordance with another aspect of the present invention, the DC coupling is not enabled until the interior antenna assembly is connected to the receiver and the receiver is powered on.